Numerous endogenous and exogenous oxidative and electrophilic chemicals such as reactive oxygen species (ROS) and nitrogen species (RNS) constantly assault the human body. Prolonged exposure to the ROS can cause oxidative damage to cells that eventually leads to chronic inflammation, a hallmark of many diseases and aging. To protect against harmful effects of the ROS, the cells use an extensive array of both endogenous (enzymes and metabolites) and exogenous (nutrients) antioxidants. Many studies have investigated the therapeutic potential of antioxidant vitamins or supplements such as vitamins C and E, carotenoids, N-acetylcysteine, and other compounds that react stoichiometrically with ROS. The results of studies involving supplemental direct antioxidants have been quite disappointing overall. This is likely because exogenous antioxidant compounds, which react stoichiometrically with oxidants, cannot be orally consumed or distributed throughout the body in large enough quantities to meet the oxidative stress demand. Additionally, redox balance in mammalian biology is maintained by endogenous enzyme systems as opposed to directly-reacted exogenous compounds.